The present invention relates to a composition useful as a bonding agent for incombustible fibrous materials and a process for preparing incombustible sheet materials. More particularly the invention relates to a bonding composition which can effectively bond incombustible fibrous materials and also becomes incombustible itself, comprising (a) a specific water-soluble polymer containing hydrazide groups or its adduct with a water-soluble alkaline earth metal salt of an inorganic acid and (b) a specific heavy metal ion, and a process for preparing incombustible materials such as paper, sheet and board using the bonding composition.
Hitherto, various inorganic fibers such as asbestos, rock wool, glass fiber, ceramic fiber, carbon fiber and metal fiber are known as incombustible fibers. Also, various bonding agents are known. However, since these known bonding agents are combustible or expensive and no incombustible and inexpensive bonding agent having an excellent bonding effect has been known, incombustible sheet materials obtained from these incombustible fibers have a decreased incombustibility or rise in price despite that some incombustible fibers are inexpensive.